In 3GPP systems, such as the General Packet Radio System (GPRS), Evolved Packet System (EPS), the downlink communication endpoint, namely the mobile or handheld wireless communication unit, referred to as user equipment (UE) in 3GPP parlance, may have multiple simultaneous connections to a number of network elements. Such network elements typically comprise gateways (GWs), such as General GPRS Support nodes (GGSNs), packet data network (PDN) GWs, etc. In addition, in latest releases of 3GPP systems, the same core network system is used in order to provide access to non-3GPP radio interfaces, such as mobile WiMAX or Wireless LAN (WLAN)
3GPP System Architecture Evolution (SAE) activity aims to devise a network architecture that will allow the convergence of multiple access technologies into a single Operator's network. This will allow users to benefit from multimode terminals that will provide seamless mobility across a number of access technologies, not necessarily defined by 3GPP, and thereby the user is able to use the most ‘appropriate’ networks at any particular point in time.
Between 3GPP systems, it is known that the 3GPP base stations, referred to as NodeBs, may be configured to broadcast other system information related to neighbouring wireless communication systems, e.g. information about the cells of the 2nd generation of mobile communications, otherwise referred to as Global System for Mobile communications (GSM) related system information.
Given the differences between technologies and mobility principles in 3GPP and non-3GPP access networks it is feasible to implement the mobility features between 3GPP and non-3GPP networks in a stepwise approach. This may allow, on the one hand, an early market entry of a basic solution and, on the other hand, a later enhancement aiming at co-operative handover decisions and context aware mobility. The latter enables a mobile node to change its point of network attachment in a secure and seamless fashion.
One non-3GPP radio access technology is known as mobile Mobile
WiMAX, as defined in the specifications Mobile WiMAX Forum™ Mobile System Profile Release 1.0 (Revision 1.4.0), May 2, 2007 Mobile WiMAX Forum™ Network Architecture Release 1.0.0, March, 2007. No mechanism is yet proposed to facilitate handover between 3GPP and non-3GPP systems.
However, in the context of 3GPP SAE discussions, the following assumptions have been decided, in order to minimize the impact to existing 3GPP legacy network elements in the radio access network (RAN) and the core network (CN):                (i) Initial release of multimode terminals will be based on a ‘dual-radio’ UE architecture. This effectively means that the UE will require duplicate circuitry, to facilitate simultaneous transmission and reception for a period of time in two different radio technologies.        (ii) Mechanisms that have traditionally been used by 3GPP, to perform network discovery for intra-3GPP systems, are based on broadcast of system information from radio access network RAN) nodes (such as radio network controller (RNC) and eNodeBs) will not be used in order not to impact the legacy network elements.        (iii) Mechanisms that have traditionally been used by 3GPP in order to perform handover decision for intra-3GPP systems and are based on network control from RAN nodes (such as RNC, eNodeBs) will also not be used in order not to impact the legacy network elements.        
Within the 3GPP SAE discussions, there has been mention of using an Access Network Discovery and Selection Function (ANDSF), which is envisaged as being an optional network device that is used to facilitate selection of both radio access technology (RAT) types (e.g. Mobile WiMAX from 3GPP and 3GPP from Mobile WiMAX). In this manner, it is envisaged that ANDSF may accelerate the handover (HO) phases and improve the UE's performance. However, as yet, there has been neither a discussion on how this is to be achieved, nor on how a UE communicates with the ANDSF.
It is also envisaged that the Mobile WiMAX system may be supported by a different Network Operator than the neighbouring 3GPP system. Thus, it is envisaged that network or resource sharing agreements may be configured between Network Operators, where different network settings, network capabilities, operating frequency bands etc. may be employed in different geographical areas.
It is known, however, in the 3GPP standard that any retrieval of policies and/or rules from the ANDSF would require the UE to transition to an ‘active’ mode of operation. As such, any information retrieval procedure should be used as rarely as possible, to ensure that a comparable performance (e.g. at least in terms of battery life) with 3GPP-only UEs.
As an alternative to using ANDSF, it is envisaged that the UE may be provided as a ‘dual-radio’ UE having two ‘radios’ on continuously, i.e. configured with duplicated circuitry to support communications in either of the dissimilar technologies. In this alternative configuration, the UE may be able to perform 3GPP to non-3GPP handover, without use of an ANDSF network device, but with reduced performance and with significant impact in the battery life of the UE.
Thus, a cellular network does not broadcast information that is not provided by the source radio access system, for example it does not broadcast an existence of another target radio access system that may be in a vicinity of the UE. In order to perform handover between different radio technologies the two radios need to be switched ‘on’ all the time in order to be able to discover the target radio system. This is an inefficient solution, since the radio circuitry in the UE needs to be able to scan all the time and of course, thereby consume significant power.
Alternatively the radio circuitry of the source system needs to be kept more frequently in an ‘active’ mode, so that it will contact the ANDSF network device more frequently and thereby be able to receive availability and configuration information about the target radio access systems in the area. This will unnecessarily consume radio resources by an UE operating in ‘active’ mode in the one radio system, as well as increase the UE's power consumption.
The aforementioned issues become more acute given the fact that, at least initially, the non-3GPP radio access systems (e.g. mobile WiMAX) will be used for ‘hotspot’ coverage providing only limited (but high-speed) coverage in a very few geographical areas. In contrast, existing 3GPP systems traditionally provide wide area coverage. Therefore, this concept of multiple overlapping coverage areas and technologies makes it even more inefficient to have the non-3GPP circuitry in the UE operational all the time, since it is going to be used only when the UE approaches these particular geographical areas.
Consequently, current techniques are suboptimal. Hence, an improved mechanism to address the problem of network discovery over a cellular network would be advantageous.